However, the 3-2 vote in favor of expanding the pipeline followed a leak of 210,000 gallons of oil just days prior. That oil gushed from a section of Keystone in South Dakota before TransCanada cut off the flow.

Plans for Keystone XL call for the pipeline to begin in Alberta's oil sands, sometimes called tar sands, and end at holding tanks in Patoka, Illinois, as well as points in Texas along the Gulf of Mexico.

Former President Barack Obama canceled the Keystone XL pipeline in November 2015 with an executive order that said it wouldn't help lower gas prices or create that many jobs. He also cited the pipeline's long-term contribution to climate change -- possibly more than 22 billion metric tons of carbon pollution, according to Scientific American.

"If we're going to prevent large parts of this Earth from becoming not only inhospitable but uninhabitable in our lifetimes, we're going to have to keep some fossil fuels in the ground," Obama said.

The XL segment already is partially built, and may ultimately cost entrepreneurs more than $10 billion. Upon completion, it would move larger volumes of oil in less time by shortening the route and burying larger-diameter pipes.

Proponents of the pipeline say it will lessen dependence on foreign oil while creating jobs. But environmental groups and many Americans -- especially American Indians -- remain furious about the project. Beyond the risk of spills, the project's steep environmental costs also include the potential industrialization of 54,000 square miles of Alberta wilderness.

"The scale and severity of what's happening in Alberta will make your spine tingle," Robert Johnson, a former Business Insider correspondent, wrote after flying over the Canadian oil sands in May 2012.

Click through to see an updated version of Johnson's photo essay, which shows the effects of Canadian oil mining -- a process in which oil-laden sand is dug from the ground, the fuel separated out, and the land converted back into use for wild plants and animals. Today that process makes up about 50% of the Keystone XL pipeline's oil, while less-visible "in situ" pumping generates the rest.

This story was originally published on March 24, 2017. It has been updated with new information.